But the
question remains, in our application, has anyone EVER put a meter between the
aircraft and the fuel nozzle to see if any static voltage exists?
Why is it not required for cars? Is there any significant difference
The gas pump is clearly grounded to the
ground, and the car has no reason to arrive at the pump with a charge relative
ground – at auto speeds there is no charge buildup due to friction with
the air that is not adequately bled off through the tires, mostly traveling
along the surfaces.
Keep in mind that the static charge of
concern is that caused by the friction between the gasoline and the hose
through which it is flowing. The important thing is having a connection
between the nozzle and the fuel in the tank. When you fuel the car the
nozzle is always in contact with the neck of the tank which is in contact with
the fuel. Any electrons stripped from the fuel by the hose easily travel back
to the fuel in the tank – no charge buildup that might cause a spark at
disconnect.
In the case of the airplane; it is possible
for there to be a residual potential difference (charge) between the ground and
the plane if the plane has just been flying at high speed. It may even be
possible that there is a residual charge of the fuel truck as a result of the
recent fueling of another plane. If the nozzle was always put in contact with
the plane away from the open tank prior to fueling (on a metal plane), and
remained in contact with the plane throughout the fueling, then the separate
ground lead really isn’t doing anything. Connecting the ground lead
to the truck (or fuel pump) prior to fueling assures that when the nozzle is
brought to the open tank there is no static discharge. Or, for example,
if the person doing the fueling decides to hold the nozzle away from contact
with the tank while fuel is flowing – like to see when the tank is
getting full (Uh, huh; we’ve seen that) – and then brings it back
in contact; that there will be no charge to make a spark.
If the plane has been sitting for period
time (I guess maybe hours), then any surface charge will have dissipated. If
you are then filling from cans, and if the can has been sitting on the ground
before you start fueling – not really a concern to bring the can to the
open tank. Then the important thing is to make sure there is a conductive path
from the fuel in the tank back to the can.
Ok, I guess I’ve probably already
said more than I know.
Be aware; be careful.
Al G